[K4] Unable to Highlight in an AZW3/KF8 Sample Downloaded from the Store

To be honest I mostly read 3rd party books and articles so far on my Kindle 4 and haven't encountered this problem. Now I just downloaded a free sample from the [UK] store and for the first time cannot highlight in it! The dictionary just works fine.

I have to add the file already went through Alf's treatment (read: have been drDRMed).

In general highlighting will work on samples, but publishers can set a limit to how much highlighting you can do, or even disable it entirely via some magic bits (this is independent of DRM). So I'm guessing that's what they have done in this case.